AN IMPROVED METHOD AND APPARATUS FOR PROVIDING A COPY-PROTECTED VIDEO SIGNAL

摘要

A anti-copy programme signal is provided. Copies of the anti-copy video puls es made on a video recorder experience reduced quality and interference in playback making them unpleasant to watch. The uncopied signal can be viewed without any material effect on picture quality. The signal comprises a pulse (28) added to each line (6) of the signal throughout both the visible pictur e region and throughout the vertical blanking region (12), as well as a first modulated wave-form (34) added to the vertical synchronisation pulses (16) o f the signal and a second modulated wave-form (36) added to several lines (6) of the picture signal before the vertical blanking section (12). The presence o f all three of these features together has been found to be provide a surprisi ng accumulative effectiveness in causing interference in the reproduction of th e modified video signal during playback of the copied video signal, that is greater than the effectiveness provided by the different features taken separately.